Engineering the chemical structure of H-shaped reactive molecules for negative dispersion of retardation

Five kinds of H-shaped reactive monomers with different central core groups were newly designed and synthesized for obtaining a negative dispersion of retardation. The H-shaped molecules were mixed with cylindrical reactive mesogen molecules and the mixtures with the H-shaped molecules wherein a benzene or a naphthalene ring is in the core presented a wide liquid crystalline phase and a uniform orientation. The retarder film made by UV-polymerization of the mixtures showed a positive or a negative dispersion of retardation depending on the chemical structure of the H-shaped molecules. To understand the different dispersion properties, the molecular orientation of the H-shaped molecules was investigated by measuring the UV-vis absorption anisotropy and out-of-plane retardation of the samples. The retarder sample showed a negative dispersion of retardation when the imine groups of the H-shaped molecules were aligned orthogonal to the slow axis of the sample.